1. Field of the Invention
The present invention relates to an organic light emitting display.
2. Discussion of Related Art
Recently, there have been various types of flat panel display devices having reduced weight and volume in comparison to cathode ray tubes. Flat panel display devices include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display devices, and organic light emitting displays, among others.
An organic light emitting display device displays images using organic light emitting diodes (OLEDs) that emit light through the recombination of electrons and holes. An organic light emitting display device has a fast response speed and is driven with low power consumption.
Generally, organic light emitting displays are divided into passive matrix OLED (PMOLED) devices and active matrix OLED (AMOLED) devices, depending on the method of driving electroluminescence (EL) elements in the displays.
An AMOLED device includes a plurality of gate lines, a plurality of data lines, a plurality of power lines and a plurality of pixels connected to the lines and arranged in a matrix form. Each of the pixels generally includes an EL element (i.e., an OLED); a switching transistor for providing a data signal; a driving transistor for driving the EL element in accordance with the data signal; and a capacitor for storing the voltage of the data signal.
An AMOLED device generally has low power consumption. However, in an AMOLED, the intensity of current that flows through the EL elements varies depending on voltage variations between gate and source electrodes of driving transistors for driving the EL elements, i.e., variations in threshold voltages of the driving transistors. Therefore, display uniformity may be compromised.
That is, characteristics of transistors provided in each of the pixels vary depending on manufacturing processes. Therefore, it is difficult to manufacture uniform transistors so that all the transistors of an AMOLED device have the same characteristics. Thus, variations in threshold voltages between pixels exist.
In order to solve these problems, compensation circuits have been recently developed. Such compensation circuits may be implemented in each pixel. However, as larger numbers of transistors and capacitors are fabricated into each pixel, it becomes more difficult to secure space in layout designs.